Instrument oil



Patented ay 13, 1941 TOIL Peter J. Wiezevich, Elizabeth, N. 3., now by judicial change of name to Peter J. Gaylor, assignor to Standard Oil Development Company, a corporation of Delaware No Drawing. Application July 15, 1936. Serial No. 90,725

dClaims.

field are entirely different from those of the com-' mon lubricating uses. For instance, watches, meters, and other fine instruments are oiled only once in a year or in several years. In order to prevent damage to the movingparts, it is therefore essential that the drop of lubricant applied remain on the parts to be lubricated, without creeping away to other portions of the instrument so as to leave a dry bearing. It is also essential that the lubricant have a low viscosity so as to penetrate into the small moving parts without interfering with the accuracy of movement at low or somewhat elevated temperature, and yet possess sufilciently low volatility so as not to evaporate during the extended period between applications. Since instruments operate in presence of air during these long periods, it is obviously necessary that the lubricant does not oxidize and become rancid so as to give rise to corrosion and other difliculties. Other properties, such as low pour point, high lubricity, etc., are also desirable in most cases.

Since such special requirements are not imposed on ordinary lubricants, it is not surprising to find that none of them are suitable for instrument use. In the first place, mineral oils of the proper viscosity are too volatile and creep too much to be of any value. Synthetic fatty esters creep even more and possess high pour points and volatility and exceptionally low viscosities. Natural fatty oils likewise creep very badly and oxidize too rapidly. There is one exception, however, and that is porpoise jaw oil. This product is unusual in the respects that it possesses only very little tendency to creep, is substantially non-volatile, and powesses the proper vicosity, with the result that it is almost univerally employed as an instrument oil. The objection to this oil is that it is exceedingly expensive, costing in the neighborhood of several hundred dollars per gallon, and is becoming even more so with the gradual extinction of the porpoise.

The present invention involves the discovery that liquid organic esters of acids of phosphorus possess the unique properties required for instrument oils. In fact, tests have shown that triortho-cresyl phosphate possesses much better non-creeping characteristics than does porpoise jaw oil itself. This is shown by the following data obtained by allowing a drop of regulated size to fall upon a polished brass plate and measuring the area of the wetted surface after standing one-half hour at 81 F.:

Area covered, sq. in.

Tri-o-cresyl phosphate 0,126 Porpoise jaw oil 1.62 Mineral refrigerator oil 1.91

As can be seen from the data, tricresyl phosphate exhibits only about one-thirteenth the creeping tendency of porpoise jaw oil, and less than one-fifteenth that of a mineral refrigerator oil of much higher viscosity.

Trl-o-cresyl phosphate possesses the following properties:

Viscosity at F. (Saybolt) seconds 132 Viscosity at 210 F seconds 39.4 Pour point ..F -20 Boiling point C 400 Specific gravity 1.179 Stability to hydrolysis Good The liquid esters of acids of phosphorus are also exceedingly stable to oxidation. For instance, in one test, a 200 g. sample of tri-o-cresyl phosphate was blown with 10 cu. ft. of air per hour at 300 F., and at the end of 8 hours the acidity was only 0.25 mg. KOH per gm. of sample, and the viscosity remained the same, while a mineral oil of seconds viscosity at 100 F. under these drastic conditions developed an acidity of 4.7 mgs. KOH per gm. and showed an increase in viscosity of 22 seconds at 100 F.

Hence, according to the present invention, it has been found that fine instruments may be successfully lubricated with liquid organic esters of acids of phosphorus, such as phosphoric or phosphorous acids. Although aliphaticfcyclic and heterocyclic esters of such acids, having pour points below -10 F., may be employed, it is found preferable to employ esters of alkylated phenols, such as tricresyl phosphate or tricresyl phosphite. Mixtures of tricresyl phosphate with triphenyl phosphate are suitable in some cases, especially the eutectic mixture. Other phosphorlc esters having low pour points which are suitable are the phenyl ortho phenyl phosphates and other esters of phosphorus disclosed in U. S. Patents 2,033,918 and 2,033,916. Amyl phosphate or isobutyl or secondary butyl phosphite may also be employed, although their volatility is higher than that of tri-ortho-cresyl phosphate. It is desirable that the viscosity of the ester or ester mixture be in the range of 100- 150 seconds Saybolt at 100 F., and in rare cases possibly to 200 seconds. 1

With such esters may be addedmineral oils to the extent of 0.5 to 5% or even as high as 10 or 25 or 50%, the guiding factor being the miscibility temperature, since the mixture should not separate into layers at temperatures as low as 10 F. or even 30 F. Since coastal, naphthenic or aromatic oils are most soluble, they are preferable when high concentrations are desired, although for lower concentrations Pennsylvania oils or synthetic hydrocarbon oils may be employed. The preferred viscosity of the mineral oil is 100-150 seconds at 100 F., and the pour should be below 0, preferably below 20 F.

Since it is sometimes diflicult to obtain a uniformly stable phosphoric ester, it is in such cases desirable to add 0.01 to 0.2% of an oxidation inhibitor, such as thio beta naphthol, diphenol disulflde, tertiary butyl phenol sulfide, triphenyl bismuth, and the like.

In order to increase the viscosity and/or viscosity index of the lubricant, soluble linear polymers or high boiling esters may be added to the extent of 0.1 to e. g. polyvinyl ethers or esters, poly acrylic or polymetacrylic esters, cellulose esters or ethers, glyceryl or glycol phosphate, and the like. Resins such as hydrocarbon resins and phenol-formaldehyde resins may likewise be dissolved therein.

Additional oiliness agents may likewise be added in concentrations of 0.1 to 5 or if desired, e. g. glycol or glyceryl esters of acids obtained by oxidation of branched hydrocarbon polymers, naphthenic acid esters, esters of aliphatic alcohols and acids of oxidized, wax, etc.

In some cases, where thicker consistency is not injurious, 'soluble metallic soaps of aluminum, cobalt, cadmium, tin, or chromium may likewise be added. The negative radicals may be stearate, naphthenate, shellate, oleate, and the like. About 0.01 to 1% of such soaps may be safely employed.

Other addition agents may be soluble dyes, especially those giving the oil the bloom and cast of petroleum lubricants, such as condensation products of aromatic or cyclic hydrocarbons.

The invention will be more clearly understood by the following examples:

Example 1 A sample of tri-ortho-cresyl phosphate had the following properties:

Viscosity Saybolt at 100 F seconds 132 Viscosity Saybolt at 210 do 39.4 Pour point F 20 It showed a lower creeping tendency than did porpoise jaw oil-and was found to be highly suitable for the lubrication of gas meters.

Example 2 The following blend is found suitable for the lubrication of fine instruments:

Percent Tricresyl phnsn'hatp 919 Glycol phthala 2.0

Dye (obtained by condensing cracking coil is eifective for lubricating large instrument bearing surfaces.

The foregoing description is illustrative of a preferred embodiment of the invention and va-- rious changes may be made within the scope of the appended claims in which it is my intention to claim the invention as broadly as the prior art permits.

- I claim:

- 1. Method of lubricating bearings of small, delicate machinery, without corrosion of bearing metals over periods of time, comprising applying essento such bearings a lubricant consisting tially of tricresyl phosphate.

2. Method of lubricating bearings of small, deli-- cate machinery, comprising applying to such bearings a lubricating medium pro-eminently consisting of the lubricant tricresyl phosphate.

3. Method of lubricating bearings of small delicate machinery without corrosion of bearing metals over periods of time, comprising applying to such bearings a lubricant consisting essentially of a liquid organic ester of an acid of phosphorus, said ester having a pour point below 0 F. and a viscosity of to 200 seconds Saybolt at 100 F. I v

4. The method according to claim-3-in which oil.

PETER J. VVIEZEVICH.

the ester contains a small amount of mineral 

